Antonio Napoli and Vittorio Curri, " Introduction to the JOCN Special Issue on Open Optical Networks", IEEE / OSA
Abstract: We provide an introduction to the paradigm of open optical networks (OON), including its evolution and benefits, followed by a brief summary of the papers in the OON special issue
H. Sun, M. Torbatian, M. Karimi, R. Maher, S. Thomson, M. Tehrani, Y. Gao, A. Kumpera, G. Soliman, A. Kakkar, M. Osman, Z. A. El-Sahn, C. Doggart, W. Hou, S. Sutarwala, Y. Wu, M. Reza Chitgarha, V. Lal, H-S. Tsai, S. Corzine, J. Zhang, J. Osenbach, S. Buggaveeti, Z. Morbi, M. Iglesias Olmedo, I. Leung, X. Xu, P. Samra, V. Dominic, S. Sanders, M. Ziari, Antonio Napoli, B. Spinnler, K.-T. Wu, P. Kandappan, "800G DSP ASIC Design Using Probabilistic Shaping and Digital Sub-Carrier Multiplexing", IEEE / OSA J. of Lightwave Technology, 2020, correspondent author
Abstract: The design of application-specific integrated circuit (ASIC) is at the core of modern ultra-high-speed transponders employing advanced digital signal processing (DSP) algorithms. This manuscript discusses the motivations for jointly utilizing transmission techniques such as probabilistic shaping and digital sub-carrier multiplexing in digital coherent optical transmissions systems. We firstly report the key-building blocks of high-speed modern DSP-based transponders working up to 800G per wave. Secondly, we show the benefits of these transmission methods in terms of system level performance. Finally, we report the first, to the best of our knowledge, long-haul experimental transmission - e.g., over 1000 km - with a real-time 7 nm DSP ASIC and digital coherent optics (DCO) capable of data rates up to 1.6 Tb/s using two waves (2x800G).
Nicola Sambo, Alessio Ferrari, Antonio Napoli, Nelson Costa, Joao Pedro, Bernd Sommerkorn-Krombholz, Piero Castoldi, Vittorio Curri, Johannes K. Fischer, Shu Namiki, Mark Filer, Vittorio Curri, ”Provisioning in Multi-band Optical Networks”, Guest editorial, IEEE / OSA J. of Lightwave Technology, invited, 2020
Abstract: Multi-band (MB) optical transmission promises to extend the lifetime of existing optical fibre infrastructures, which usually transmit within the C-band only, with C ++ L-band being also used in a few high-capacity links. In this work, we propose a physical-layer-aware provisioning scheme tailored for MB systems. This solution utilizes the physical layer information to estimate, by means of the generalized Gaussian noise (GGN) model, the generalized signal-to-noise ratio (GSNR). The GSNR is evaluated assuming transmission up to the entire low-loss spectrum of optical fiber, i.e., from 1260 to 1625 nm. We show that MB transmission may lead to a considerable reduction of the blocking probability, despite the increased transmission penalties resulting from using additional optical fiber transmission bands. Transponders supporting several modulation formats (polarization multiplexing – PM – quadrature phase shift keying – PM-QPSK –, PM 8 quadrature amplitude modulation – PM-8QAM –, and PM-16QAM) from O- to L-band are considered. An increase of the accommodated traffic with respect to the C-band transmission only case, ranging from about four times with S ++ C ++ L-band and up to more than six times when transmitting from E to L-band is reported.
Alessio Ferrari, Antonio Napoli, Johannes K. Fischer, Nelson Costa, Andrea D’Amico, Jõao Pedro, Wladek Forysiak, Erwan Pincemin, Andrew Lord, Alexandros Stavdas, Juan Pedro F.-P. Gimenez, Gunther Roelkens, Nicola Calabretta, Silvio Abrate, Bernd Sommerkorn-Krombholz, Vittorio Curri, "The Achievable Capacity of Multi-band Transmission Systems Using ITU-T G.652.D Optical Fibers", IEEE / OSA Journal of Lightwave Technology, 2020
Abstract: Fiber-optic multi-band transmission (MBT) aims at exploiting the low-loss spectral windows of single-mode fibers (SMFs) for data transport, expanding by ~11 times the available bandwidth of C-band line systems and by ~5 times C+L-band line systems'. MBT offers a high potential for cost-efficient throughput upgrades of optical networks, even in absence of available dark-fibers, as it utilizes more efficiently the existing infrastructures. This represents the main advantage compared to approaches such as multi-mode/-core fibers or spatial division multiplexing. Furthermore, the industrial trend is clear: the first commercial C+L-band systems are entering the market and research has moved toward the neighboring S-band. This article discusses the potential and challenges of MBT covering the ITU-T optical bands O -> L. MBT performance is assessed by addressing the generalized SNR (GSNR) including both the linear and nonlinear fiber propagation effects. Nonlinear fiber propagation is taken into account by computing the generated nonlinear interference by using the generalized Gaussian-noise (GGN) model, which includes the interaction of nonlinear fiber propagation with stimulated Raman scattering (SRS), and in general considers wavelength-dependent fiber parameters. For linear effects, we hypothesize typical components' figures and discussion on components' limitations, such as transceivers', amplifiers' and filters' are not part of this work. We focus on assessing the transmission throughput that is realistic to achieve by using feasible multi-band components without specific optimizations and implementation discussion. So, results are meant to address the potential throughput scaling by turning-on excess fiber transmission bands. As transmission fiber, we focus exclusively on the ITU-T G.652.D, since it is the most widely deployed fiber type worldwide and the mostly suitable to multi-band transmission, thanks to its ultra-wide low-loss single-mode high-dispersion spectral region. Similar analyses could be carried out for other single-mode fiber types. We estimate a total single-fiber throughput of 450 Tb/s over a distance of 50 km and 220 Tb/s over regional distances of 600 km: ~10 times and 8 times more than C-band transmission respectively and ~2.5 times more than full C+L
Antonio Napoli, Johannes K. Fischer, Shu Namiki, Mark Filer, Vittorio Curri, "Guest Editorial Ultra Wideband WDM Systems", Guest editorial, IEEE / OSA J. of Lightwave Technology, guest editorial, 2020
B. Spinnler, A. X. Lindgren, U. Andersen, S. Melin, J. Slovak, W. Schairer, K. Pulverer, J. Martensson, E. De Man, G. Khanna, R. H. Derksen, J. Steinmayer, R. Jozapovics, J. Blume, T. Lemström, J. Christensen, U. Häbel, U. Bauer, Antonio Napoli, and B. Sommerkorn-Krombholz, ", IEEE / OSA J. of Optical Communications and Networking, 2019
Abstract: We introduce a new transponder type for optical networks referred to as autonomous intelligent transponder (AIT) capable of autonomously adapting transmission parameters to the quality of the link over which it is transmitting. This novel concept fills one of the main gaps toward the realization of flexible and aware optical networks. We present experimental results to validate the AIT concept as part of a field trial in Telia Carrier’s live optical European backbone network
L. Velasco, A. Chiadò Piat, O. González, A. Lord, Antonio Napoli, P. Layec, D. Rafique, A. D’Errico, D. King, M. Ruiz, F. Cugini, and R. Casellas, "Monitoring and Data Analytics for Optical Networking: Benefits, Architectures, and Use Cases", IEEE Networks
Abstract: Operators’ network management continuously measure network health by collecting data from the deployed network devices; data is used mainly for performance reporting and diagnosing network problems after failures, as well as by human capacity planners to predict future traffic growth. Typically, these network management tools are generally reactive and require significant human effort and skills to operate effectively. As optical networks evolve to fulfil highly flexible connectivity and dynamicity requirements, and supporting ultra-low latency services, they must also provide reliable connectivity and increased network resource efficiency. Therefore, reactive human-based network measurement and management will be a limiting factor in the size and scale of these new networks. Future optical networks must support fully automated management, providing: i) dynamic resource re-optimization to rapidly adapt network resources based on predicted conditions and events; ii) identify service degradation conditions that will eventually impact connectivity and highlight critical devices and links for further inspection; and iii) augment rapid protection schemes if a failure is predicted or detected, and facilitate resource optimization after restoration events. Applying automation techniques to network management requires both the collection of data from a variety of sources at various time frequencies, but it must also support the capability to extract knowledge and derive insight for performance monitoring, troubleshooting, and maintain network service continuity. Innovative analytics algorithms must be developed to derive meaningful input to the entities that orchestrate and control network resources; these control elements must also be capable of proactively programming the underlying optical infrastructure. In this article, we review the emerging requirements for optical network management automation, the capabilities of current optical systems, and the development and standardization status of data models and protocols to facilitate automated network monitoring. Finally, we propose an architecture to provide Monitoring and Data Analytics (MDA) capabilities, we present illustrative control loops for advanced network monitoring use cases, and the findings that validate the usefulness of MDA to provide automated optical network management
Yaron Yoffe, G. Khanna, E. Wohlgemuth, E. de Man, B. Spinnler, N. Hanik, A. Napoli, D. Sadot, "Low Resolution Digital Pre-Compensation Enabled by Digital Resolution Enhancer", top scored paper, invited, IEEE / OSA J. of Lightwave Technology
Abstract: Digital pre-compensation (DPC) is an indispensable block of state-of-the-art optical transceivers, and a key enabler for high order modulation formats (HOMFs) transmission. A crucial component, which enables the transmission of the pre-compensated HOMFs, is the digital-to-analog-converter (DAC). However, as data and symbol-rates grow, the implementation of such devices becomes highly challenging in terms of performance, power consumption and costs. In this work, a digital-resolution-enhancer (DRE) algorithm is discussed, conjoined with high-end DPC methods. Simulation results demonstrate that the DRE reduces the effect of DAC quantization noise power by more than 8 dB for the considered cases of 400G with 64QAM. The proposed scheme is experimentally verified by transmitting a 4-bit DP-64QAM 400Gbit/s signal in a WDM scenario over 95 km of single mode fiber.
Juraj Slovak, M. Herrmann, W. Schairer, E. Torrengo, K. Pulverer, Antonio Napoli, U. Haebel, Aware Optical Networks: Leaving the Lab, OSA / IEEE J. of Optical Communications and Networking, invited, 2019
Abstract: Awareness of optical network performance and its accurate prediction enable squeezing of margins allocated for stable operation. We discuss the potential of online performance assessment by leveraging bandwidth-variable transponders in flexible optical networks, and quantify its benefit by simulating the total capacity of typical long-haul networks. An experimental analysis in a system lab and a field trial demonstrate the viability and remarkable accuracy of the presented technologies in a live network. Finally, we analyze the impact of disaggregated networks on performance awareness.
Abstract: Digital pre-compensation techniques are among the enablers for cost-efficient high-capacity transponders. In this paper we describe various methods to mitigate the impairments introduced by state-of-the-art components within modern optical transceivers. Numerical and experimental results validate their performance and benefits.
Abstract: We present a digital pre-distortion (DPD) technique to compensate for IQ-Mach-Zehnder modulators with finite extinction ratio (ER). The proposed method significantly improves the system performance by reducing the impairments introduced by the component imperfections. Our technique is performed in two steps: First, the arcsin pre-distorts the nonlinear sinusoidal transfer function of the modulator; Second, a constrained optimization method that utilizes the gradient descent algorithm pre-distorts the modulator driving signals, thus mitigating the distortion induced by finite ER. Since the optimal gradient calculation is rather complex, we introduce a simplified polynomial-based approximation that achieves comparable performance. The DPD gain is assessed via numerical simulations by varying modulation format and ER in an optical back-to-back configuration. The results are presented as required optical signal-to-noise ratio versus the modulator output power (PMZM ) normalized with respect to the MZM input power (continuous wave of the laser, PCW ). A considerable improvement is showed when compared to the case without DPD or with the arcsin module for ERs ≤ 20 dB and 32/64QAM.
Abstract: We report on the results of a field trial carried out on a Telecom Italia (TI) metro link, targeting short data center interconnect (DCI) applications. The test-bed presented realistic transmission conditions such as an average ~0.3 dB/km attenuation and usage of legacy EDFA-only. We transmitted a net bit rate of 400 Gb/s on a single carrier with 64 quadrature amplitude modulation (QAM) and 128QAM over 156 km. Errorfree transmission over 80 km for single carrier DWDM 30x400G 64QAM and 30x400G 128QAM (one half of the C-Band) is reported. The net spectral efficiency, for both schemes, is 7.11 bit/s/Hz.
Abstract: This short introductory paper sets the scene for this special edition of the Journal of Optical Communications and Networking , which is focused on elastic optical networks (EONs). A brief overview of the field is given, followed by a summary of the five invited papers. This special edition is designed to provide a review of current EON technology.
Benoit Clouet, Joao Pedro, Nelson Costa, Maxim Kuschnerov, Anton Schex, Juraj Slovak, Danish Rafique, Antonio Napoli, "Networking Aspect for Next Generation Elastic Optical Interfaces", OSA Journal of Optical Communications and Networking, 2016
Abstract: Next-generation elastic optical interfaces will support a wide range of line rates and modulation formats. Such transmission schemes enable doubling of the channel capacity at the expense of a lower reach, whereas a flexible DWDM grid supports the transport of multiple optical signals within a single frequency slot by packing them closely, thus saving spectral resources. The resulting multitude of options on the line side provides network planners the capability to derive the most suitable one for each individual path inside the network. However, planning and operational complexity should not be overlooked, since aspects such as added spectrum fragmentation can hamper the expected network improvements. This paper investigates how to obtain the best compromise between harnessing the main benefits of next-generation optical interfaces, while keeping the complexity of the underlying system at a reasonable level. In particular, we define a novel network spectral efficiency (SE) metric that enables, on one hand, to highlight the relevance of supporting a flexible grid to improve SE and, on the other hand, to demonstrate that the grid granularity can be based on coarser 50 GHz increments without major penalties. The effectiveness of this parameter has been verified by considering two reference network topologies. Finally, the paper also discusses how future optical interface technology developments will shape network design.
Abstract: This paper describes the problematic filter narrowing effect in the context of next-generation elastic optical networks. First, three possible scenarios are introduced: the transition from an actual fixed-grid to a flexi-grid network, the generic full flexi-grid network, and a proposal for a filterless optical network. Next, we investigate different transmission techniques and evaluate the penalty introduced by the filtering effect when considering Nyquist wavelength division multiplexing, single side-band direct-detection orthogonal frequency division multiplexing, and symbol-rate variable dual polarization quadrature amplitude modulation. Also, different approaches to compensate for the filter narrowing effect are discussed. Results show that the specific needs per each scenario can be fulfilled by the aforementioned technologies and techniques or a combination of them, when balancing performance, network reach, and cost.
Abstract: Increase in transmission symbol-rate as well as order of quadrature amplitude modulation (QAM) is identified as the most economical way to reduce cost per transmitted bit. In particular, next generation transponders aim at supporting data-rates up to 1 Tb/s employing superchannels due to electrical components' bandwidth limitations. Furthermore, the introduction of a flexible-grid architecture can maximize throughput by minimizing spectral gaps in available optical spectrum. Keeping in view these design options, we conducted several high capacity experiments with tier1 operator Orange using their field deployed standard single mode fiber (SSMF, G.652), having a total length of 762 km, connecting the cities Lyon and Marseille in France. In particular we employed four subcarriers per Tb/s superchannel, each modulated by PM-16QAM, PM-32QAM, and PM-64QAM with per carrier symbol-rates of 41.2 GBd, 33 GBd, and 34 GBd, respectively. The subcarrier spacing was 50 GHz for the PM-16QAM case and 37.5 GHz for both the PM-32QAM and PM-64QAM cases allowing in total 24 × 1.0, 32 × 1.0, and 32 × 1.2 Tb/s superchannels over C-band and resulting in potential C-band capacities of 24.0, 32.0, and 38.4 Tb/s, respectively. After field transmission the maximum available OSNR0.1 nm margin compared to the required OSNR0.1 nm at forward error correction (FEC) threshold was 8.2, 5.4, and 4.2 dB for PM-16QAM, PM-32QAM, and PM-64QAM, respectively. The transmission reach for PM16QAM and PM-32QAM modulated superchannels was extended to ~1571 and ~1065 km using erbium doped fiber amplified SSMF spans of ~101 km length.
Abstract: In this paper, we present a novel digital preemphasis algorithm to compensate for the electrical bandwidth limitations at the transceiver also by taking into account the quantization noise introduced by the signal digitalization. The proposed method is based on the minimization of the mean square error between the desired input signals and the output signals of the digital-to-analog converter/analog-to-digital converter (DAC/ADC), when assuming the knowledge of the DAC/ADC frequency responses. Though this paper focuses on the DAC/ADC compensation, the introduced method could be applied to electrical bandwidth limitations caused by any other component within the transponder. The performance of the algorithm is assessed in optical back-to-back configuration by comparing it against the case without digital preemphasis and with a previously published method to compensate for DAC bandwidth limitations. Our analysis shows that when utilizing realistic descriptions of the DAC/ADC, the proposed digital preemphasis (at the transmitter) or digital compensation (at the transmitter and receiver) can considerably increase the maximum transmittable symbol rate for the case of advanced modulation formats. For example, the maximum symbol rate can be ideally increased up to ~ 60% for the case of 16QAM when employing the high-speed DAC with a -3 dB electrical bandwidth of ~16 GHz and with six effective number of bits. Furthermore, we evaluate the impact of additional noise sources, based on experimental measurements, envisioning potential for further improvements of the digital preemphasis module. Finally, we experimentally verified our algorithm, for the specific case of polarization-multiplexed 16QAM, showing a considerable match between simulation and lab results.
Abstract: The operation of multi-domain and multi-vendorEONs can be achieved by interoperable Sliceable BandwidthVariable Transponders(SBVTs), a GMPLS / BGP-LS-basedcontrol plane and a planning tool. The control plane is extendedto include the control of SBVTs and EXCs, enablingthe end-to-end provisioning and recovery of network services. A multi-partnertestbed is built to demonstrate and validate the proposedend-to-end architecture.Interoperability among S-BVTs isexperimentally tested between different implementations. In thiscase, transponders are configured using the proposed controlplane. The achieved performancewith hard-decision and soft-decision FECs using only the information distributed by thecontrol plane is measured against the performance of single-vendor implementation, where proprietary information is used,demonstrating error-free transmission up to 300 km.
Gianluca Meloni, Talha Rahman, Antonio Napoli, Francesco Fresi, Nicola Sambo, Antonio D’Errico, Danish Rafique, Markus Nölle, Huug de Waardt, Marc Bohn, and Luca Potí, "Experimental Comparison of Transmission Performance for Nyquist WDM and Time-Frequency Packing", IEEE / OSA Journal of Lightwave Technology, 2015
Abstract: We present a linear and nonlinear digital pre-distortion (DPD) tailored to the components of an optical transmitter. The DPD concept uses nonlinear models of the transmitter devices, which are obtained from direct component measurements. While the digital-to-analog converter and driver amplifier are modeled jointly by a Volterra series, the modulator is modeled independently as a Wiener system. This allows for block-wise compensation of the modulator by a Hammerstein system and a pre-distortion of the electrical components by a second Volterra series. In simulations and extensive experiments, the performance of our approach for nonlinear DPD is compared to an equivalent linear solution as well as to a configuration without any digital pre-distortion. The experiments were performed using M-ary quadrature-amplitude modulation (M-QAM) formats ranging from 16-QAM to 128-QAM at a symbol rate of 32 GBd. It is shown that DPD improves the required optical signal-to-noise ratio at a bit error ratio of 210 -2 by at least 1.2 dB. Nonlinear DPD outperforms linear DPD by an additional 0.9 dB and 2.7 dB for higher-order modulation formats such as 64-QAM and 128-QAM, respectively.
Matthias Gunkel, Arnold Mattheus, Felix Wissel, Antonio Napoli, Joao Pedro, Nelson Costa, Talha Rahman, Gianluca Meloni, Francesco Fresi, Filippo Cugini, Nicola Sambo, and Marc Bohn, "Vendor-Interoperable Elastic Optical Interfaces – standards, experiments and challenges", invited, OSA Journal of Optical Communications and Networking, 2015
D. Rafique, T. Rahman, Antonio Napoli, R. Palmer, J. Slovak, E. De Man et al. , "9.6 Tb/s CP-QPSK Transmission Over 6500 km of NZ-DSF With Commercial Hybrid Amplifiers", IEEE Photonics Technology Letters, 27(18), 1911-1914.
T. Rahman, D. Rafique, Antonio Napoli, B. Spinnler, M. Kuschnerov, C. Okonkwo, H. de Waardt, A. M. J. Koonen, "Ultra-Long Haul 1.28 Tb/s PM-16QAM WDM Transmission Employing Hybrid Amplification", IEEE / OSA Journal of Lightwave Technology, 2015
Abstract: In this work we detail the strategies adopted in the European research project IDEALIST to overcome the predicted data plane capacity crunch in optical networks. In order for core and metropolitan telecommunication systems to be able to catch up with Internet traffic, which keeps growing exponentially, we exploit the elastic optical networks paradigm for its astounding characteristics: flexible bandwidth allocation and reach tailoring through adaptive line rate, modulation formats, and spectral efficiency. We emphasize the novelties stemming from the flex-grid concept and report on the corresponding proposed target network scenarios. Fundamental building blocks, like the bandwidth-variable transponder and complementary node architectures ushering those systems, are detailed focusing on physical layer, monitoring aspects, and node architecture design.
E. Hugues-Salas, G. Zervas, D. Simeounidou, E. Kosmatos, T. Orphanoudakis, A Stavdas, M. Bohn, Antonio Napoli, T. Rahman, F. Cugini, N. Sambo, S. Frigerio, A. D’Errico, A. Pagano, E. Riccardi, V. Lopez, J. P. F.-P. Gimenez„ "Next Generation Optical Nodes: the Vision of the European Research Project IDEALIST", IEEE Communications Magazine, 2015
Danish Rafique, Antonio Napoli, Stefano Calabrò, and Bernhard Spinnler, "Digital Pre-Emphasis in Optical Communication Systems: On the DAC Requirements for Terabit Transmission Applications", IEEE / OSA Journal of Lightwave Technology, 2015
Abstract: This article reports the work on next generation transponders for optical networks carried out within the last few years. A general architecture supporting super-channels (i.e., optical connections composed of several adjacent subcarriers) and sliceability (i.e., subcarriers grouped in a number of independent super-channels with different destinations) is presented. Several transponder implementations supporting different transmission techniques are considered, highlighting advantages, economics, and complexity. Discussions include electronics, optical components, integration, and programmability. Application use cases are reported.
Abstract: Next-generation coherent optical systems are geared to employ high-speed digital-to-analog converters (DAC), allowing for digital pre-processing of the signal and flexible optical transport networks. However, one of the major obstacles in such architectures is the limited resolution (less than 5.5 effective bits) and -3dB bandwidth of commercial DACs, typically limited to half of the current baud rates, and even relatively reduced in case of higher baud rate transponders (400Gb/s and 1Tb/s). In this paper, we propose a simple digital pre-emphasis (DPE) algorithm to compensate for DAC induced signal distortions, and exhaustively investigate the impact of DAC specifications on system performance, both with and without DPE. As an outcome, performance improvements are established across various DAC hardware requirements (effective number of bits and bandwidth) and channel baud rates, for m-state quadrature amplitude modulation (QAM) formats. In particular, we show that lower-order modulation formats are least affected by DAC limitations, however they benefit the most from DPE in extremely challenging hardware conditions. On the contrary, higher order formats are severely limited by DAC distortions, and moderately benefit from DPE across a wide range of DAC specifications. Moreover, effective number of bit requirements are established for m-state QAM, assuming low and high baud rate transmission regimes.
Finally, we discuss the application scenarios for the proposed DPE in next-generation terabit systems, and establish maximum transportable baud rates, which are shown to be used towards increasing channel baud rates to reduce terabit subcarrier count or towards increasing forward error correction (FEC) overheads to reduce the pre-FEC bit error rate threshold. Maximum baud rates after DPE are summarized here for polarization multiplexed BPSK, QPSK, 8QAM and 16QAM, assuming two DACs: Current commercial DACs (5.5 effective bits, 16GHz bandwidth) 57Gbaud, 54Gbaud, 51Gbaud, and 48Gbaud, respectively. Next-generation DACs (7 effective bits, 22GHz bandwidth): 62Gbaud, 61Gbaud, 60Gbaud, and 58Gbaud, respectively.
Abstract: In this letter, we report on 400 Gb/s polarization multiplexed 16-state quadrature amplitude modulation (PM-16QAM) transponder variants and flex-grid network upgrade configurations. We address transponder subcarrier granularity, and demonstrate that the performance improvement, from dual-carrier to quad-carrier super-channel configuration, is limited to ~ 1.4 dB (in Q-factor, at power spectral density of 10-1 mW/GHz), at the cost of doubled hardware requirements. In view of that, we establish the performance improvements, for a dual-carrier 400 Gb/s PM-16QAM transceiver, as a function of increasing forward error correction overhead (FEC-OH) and spectral inversion based super-channel fiber nonlinearity compensation (SNLC-SI). We show that increasing the FEC-OH improves the transmission performance, at the cost of significant power consumption requirements, alternatively, employing SNLC-SI, at a lower FEC-OH, is a more power efficient solution. In particular, for homogeneous and heterogeneous launch power based network configurations, SNLC-SI enables ~ 23% and ~ 45% reach improvements at maximum considered FEC-OH (45%). At a fixed distance, it enables ~ 25% and ~ 50% power savings, respectively, compared with FEC-OH employing linear compensation only.
Abstract: Flex-grid optical networks have evolved as a near-future deployment option to facilitate dynamic and bandwidth intense traffic demands. These networks enable capacity gains by operating on a flexible spectrum, allocating minimum required bandwidth, for a given channel configuration. It is thus important to understand the nonlinear dynamics of various high bit-rate super-channel configurations, and whether such channels should propagate homogenously (uniform channel configuration) or heterogeneously (non-uniform channel configuration), when upgrading the current static network structure to a flex-grid network. In this paper, we report on the spectrum allocation strategies based on the impact of inter-channel fiber nonlinearities, for PM-16QAM channels (240Gb/s, 480Gb/s and 1.2Tb/s) –termed as super-channels, propagating both homogenously, and heterogeneously with 120Gb/s PM-QPSK, 43Gb/s PM-QPSK, and 43Gb/s DPSK traffic. In particular, we show that for high dispersion fibers, both homogenous and heterogeneous spectrum allocation enable similar performance, i.e. the nonlinear impact of hybrid traffic is found to be minimal (less than 0.5dB relative penalties). We further report that in low dispersion fibers, the impact of spectrum allocation is more pronounced, and heterogeneous traffic employing 120Gb/s PM-QPSK neighbors enables the best performance, ~0.5dB better than homogenous transmission. However, the absolute nonlinear impact of co-propagating traffic is more significant, compared to high dispersion fibers, with maximum performance penalties up to 1.5dB.
Abstract: We report on the nonlinear transmission limits of various super-channel configurations in a flex-grid network upgrade scenario. In particular, we consider flexible data-rates ranging from 180Gb/s to 1.2Tb/s, employing either single-carrier, dual-carrier, or penta-carrier polarization multiplexed m-state quadrature amplitude modulation (PM-8QAM/PM-16QAM) –termed as super-channels, and establish transmission performance margins for each configuration, both with and without super-channel fiber nonlinearity compensation. Our results show that the benefit of intra super-channel nonlinearity mitigation (nonlinear compensation addressing full super-channel bandwidth) reduces with increasing sub-carrier count within the super-channel, and that single-carrier super-channel achieves the maximum improvement from nonlinearity mitigation (up to ~4.5dB, in Q-factor), better than dual-carrier (up to ~3.5dB) and penta-carrier (up to ~2dB) configurations. Moreover, the maximum reach improvement, compared to linear compensation only, is found to be ~170% (180Gb/s, PM-8QAM), ~150% (240Gb/s, PM-16QAM), ~100% (360Gb/s, PM-8QAM), ~100% (480Gb/s, PM-16QAM), and ~65% (1.2Tb/s, PM-16QAM).
Abstract: Next-generation optical communication systems will continue to push the (bandwidth · distance) product towards its physical limit. To address this enormous demand, the usage of digital signal processing together with advanced modulation formats and coherent detection has been proposed to enable data-rates as high as 400 Gb/s per channel over distances in the order of 1000 km. These technological breakthroughs have been made possible by full compensation of linear fiber impairments using digital equalization algorithms. While linear equalization techniques have already matured over the last decade, the next logical focus is to explore solutions enabling the mitigation of the Kerr effect induced nonlinear channel impairments. One of the most promising methods to compensate for fiber nonlinearities is digital back-propagation (DBP), which has recently been acknowledged as a universal compensator for fiber propagation impairments, albeit with high computational requirements. In this paper, we discuss two proposals to reduce the hardware complexity required by DBP. The first confirms and extends published results for non-dispersion managed link, while the second introduces a novel method applicable to dispersion managed links, showing complexity reductions in the order of 50% and up to 85%, respectively. The proposed techniques are validated by comparing results obtained through post-processing of simulated and experimental data, employing single channel and WDM configurations, with advanced modulation formats, such as quadrature phase shift keying (QPSK) and 16-ary quadrature amplitude modulation (16-QAM). The considered net symbol rate for all cases is 25 GSymbol/s. Our post-processing results show that we can significantly reduce the hardware complexity without affecting the system performance. Finally, a detailed analysis of the obtained reduction is presented for the case of dispersion managed link in terms of number of required complex multiplications per transmitted bit.
Abstract: The world is connected by a core network of long-haul optical communication systems that link countries and continents, enabling long-distance phone calls, data-center communications, and the Internet. The demands on information rates have been constantly driven up by applications such as online gaming, high-definition video, and cloud computing. All over the world, end-user connection speeds are being increased by replacing conventional digital subscriber line (DSL) and asymmetric DSL (ADSL) with fiber to the home. Clearly, the capacity of the core network must also increase proportionally.
Abstract: Wavelength selective switches (WSSs) that are integrated in reconfigurable optical add-drop multiplexers (ROADMs) induce penalties on the optical signal due to tight optical filtering, which increases as several ROADMs are cascaded in a meshed network. In this letter, we propose and analyze possible configurations for the mitigation of these penalties in optical domain using optical wave shaper (WS). Including one WS in every ROADM node allows transmission of 28 and 32 GBd signals, which are QPSK, 8-QAM, or 16-QAM modulated, through a cascade of 32 and 14 WSS filters, respectively. With an average bandwidth of 33 GHz per WSS, an optical signal to noise ratio penalty below 1 dB at BER=1×10-3 is observed.
Abstract: Spatial-division multiplexing in the form of few-mode fibers has captured the attention of researchers since it is an attractive approach to significantly increase the channel capacity. However, the optical components employed in such systems introduce mode-dependent loss or gain (MDL) due to manufacturing imperfections, leading to significant system impairments. In this work the impact of MDL from optical amplifiers in few-mode fibers with either weak or strong mode coupling is analyzed for a 3x136-Gbit/s DP-QPSK mode-division multiplexed transmission system. It is shown that strong mode coupling reduces the impact of MDL in a similar manner as that polarization-dependent loss is reduced in single mode fibers by polarization-mode dispersion.
Abstract: Spatial-division multiplexing in the form of few-mode fibers has captured the attention of researchers since it is an attractive approach to significantly increase the channel capacity. However, the optical components employed in such systems introduce mode-dependent loss or gain (MDL) due to manufacturing imperfections, leading to significant system impairments. In this work the impact of MDL from optical amplifiers in few-mode fibers with either weak or strong mode coupling is analyzed for a 3x136-Gbit/s DP-QPSK mode-division multiplexed transmission system. It is shown that strong mode coupling reduces the impact of MDL in a similar manner as that polarization-dependent loss is reduced in single mode fibers by polarization-mode dispersion.
Abstract: We compare the transmission performance of 112-Gb/s POLMUX-QPSK modulation over large-Aeff Pure-Silica core fiber and SSMF using EDFA-only amplification. The higher nonlinear threshold of the large-Aeff Pure-Silica core fiber allows for a 55% increase in transmission distance. By using back-propagation an additional 10% increase is observed. In case spans with equal length for both fiber types and two splices per span only would have been used, resulting in a lower span loss for the large-Aeff Pure-Silica core fiber, the total increase grows to 85%.
M. Kuschnerov, K. Piyawanno, M. S. Alfiad, B. Spinnler, Antonio Napoli, B. Lankl, "Impact of Mechanical Vibrations on Laser Stability and Carrier Phase Estimation in Coherent Receivers", IEEE Photonics Technology Letters, 2010
M. Kuschnerov, K. Piyawanno, B. Spinnler, M. S. Alfiad, Antonio Napoli, B. Lankl, "Data-Aided Single-Carrier Coherent Receivers", invited, IEEE Photonics Journal, 2010
M. Kuschnerov, M. Chouayakh, K. Piyawanno, B. Spinnler, M. S. Alfiad, Antonio Napoli, and B. Lankl, "On the Performance of Coherent Systems in Presence of Polarization-Dependent Loss, IEEE Photonics Technology Letters, 2010
M. Kuschnerov, F. N. Hauske, B. Spinnler, Antonio Napoli, B. Lankl, "DSP Algorithms for Single Carrier Coherent Optical Receivers", IEEE / OSA Journal of Lightwave Technology, 2009
M. S. Alfiad, D. v. d. Borne, F. Hauske, Antonio Napoli, A. M. J. Koonen, H. de Waardt, "Maximum Likelihood Sequence Estimation for Optical Phase-Shift Keyed Modulation Formats", IEEE / OSA Journal of Lightwave Technology, 2009
M. S. Alfiad, D. v. d. Borne, S. Jansen, T. Wuth, M. Kuschnerov, G. Grosso, Antonio Napoli, H. de Waardt, "A comparison of Electrical and Optical Dispersion Compensation for 111-Gbit/s POLMUX-RZ-DQPSK", IEEE / OSA Journal of Lightwave Technology, 2009
M. S. Alfiad, M. Kuschnerov, T. Wuth, T.J. Xia, G. Wellbrock, E.D. Schmidt, D. van den Borne, B. Spinnler, C.J. Weiske, E. de Man, Antonio Napoli , M. Finkenzeller, S. Spaelter, M. Rehman, J. Behel, M. Chbat, J. Stachowiak, D. Peterson, W. Lee , M. Pollock, B. Basch, D. Chen, M. Freiberger, B. Lankl, and H. de Waardt, "111-Gb/s Transmission over 1040-km Field-Deployed Fiber with 10G/40G Neighbors", IEEE Photonics Technology Letters, 2009. The results contained in this paper were awarded by Nokia Siemens Networks with the NSN Quality Award 2009 for Innovation.
M. S. Alfiad, D. v.d Borne, F. Hauske, Antonio Napoli, B. Lankl, T. Koonen, H. de Waardt, "A DPSK receiver with Enhanced CD Tolerance through Optimized Demodulation and MLSE", IEEE Photonics Technology Letters, 2008
Antonio Napoli, V. Curri, R. Gaudino, P. Poggiolini, "Electronic equalization for advanced modulation formats in dispersion-limited systems", IEEE Photonics Technology Letters, 2004
M. Strasser, P. J. Winzer, Antonio Napoli, "Noise and intersymbol-interference properties of OTDM and ETDM receivers", IEEE Photonics Technology Letters, 2004